1. Field of the Invention
The present invention relates to discrete bipolar transistors, and in particular relates to such transistors which are fabricated in a manner so as to obtain fixed, controllable gain characteristics.
2. Description of the Prior Art
Dual collector lateral PNP transistors are well known in the integrated circuit art. When one of the collectors of a dual collector lateral PNP transistor is tied back to the base of the same transistor, the current flowing out of the base and that collector closely duplicates the current flowing from the other, independent collector. Thus, if a fixed current is caused to flow through the first collector which is tied to the base, the free collector becomes a constant current source over reasonable values of load resistance.
In these integrated circuit arrangements, the two collectors generally take the form of hemispherical rings partially encircling the emitter, such that equal injection occurs across the emitter-base junction in the direction of each collector. Such devices are used quite extensively in linear integrated circuits where tight current tolerances are required.
There are also suggestions in the prior art for utilizing independent collectors in discrete Bipolar transistors. See, for example, U.S. Pat. No. 3,074,003 to Luscher; and U.S. Pat. No. 3,134,026 to Earle.
In U.S. Pat. No. 3,626,313, Zuk discloses a monolithic integrated circuit employing a dual collector arrangement, in which one collector is tied back to the base of the same transistor. A similar arrangement is disclosed in U.S. Pat. No. 3,822,387 to Mulder.